The use of DNA samples (DNA=deoxyribonucleic acid), and particularly microarrays of such samples, provides an important technology in research for the simultaneous analysis of thousands of genes. This technology includes the immobilization of DNA samples from many genes on a fixed substrate surface, for example on a glass slide for a light microscope. The DNA samples are preferably arranged in an array of sample spots or “spots”, i.e., in a two-dimensional grid on the substrate, and the origin of a corresponding DNA sample may be determined later based on the specific position within such an array. The technology typically includes contacting the DNA sample array with RNA specimen suspensions and/or solutions (RNA=ribonucleic acid) in order to thus determine specific nucleotide sequences in the DNA samples. In order to be able to differentiate between different RNA specimens, they are often provided with a “tag” or “label”, i.e., a molecule which emits a fluorescent light having a specific wavelength corresponding to the respective special RNA specimen.
Under good experimental conditions, the RNA specimen hybridizes and/or binds to the immobilized DNA samples and forms hybrid DNA-RNA strands together with them. Differences in hybridization among the DNA samples may be determined for each of the immobilized DNA samples and for special RNA specimens by measuring the intensity and wavelength dependence of the fluorescence of each individual microarray element and it may thus be found out whether the degree of gene expression varies in the DNA samples investigated. Using DNA microarrays, statements may thus be made about the expression of great numbers of genes and about their expression pattern, although only small amounts of biological material have to be used.
DNA microarrays have established themselves as a successful tool and the devices for performing DNA hybridization have been improved continuously (cf., for example, U.S. Pat. No. 6,238,910 or WO 00/09650). This document discloses a device to provide a hybridization chamber for hybridizing nucleic acid samples on a slide, which is implemented to be movable in relation to this slide and includes an annular seal for sealing the hybridization chamber by being applied to the surface of this slide. In addition, the device disclosed includes lines for supplying and/or removing media to and/or from the hybridization chamber, as well as a sample supply line. An improved temperature control and a movement of the liquid having the RNA specimens in relation to the DNA samples immobilized on the slide is also disclosed. However, it takes too long until an adequately good distribution of the specimen liquid in relation to the samples immobilized on the surface of the slide is achieved, and, in addition, the consumption of specimen liquid is considered to be too high.